How to CREATE TABLE ... LIKE without the NOT NULL Constraints?

Try this:

CREATE TABLE my_table_bk
AS
  SELECT *
  FROM my_table
  WHERE false;

Or, you can append LIMIT 0 instead of the WHERE clause.

This will create a table my_table_bk with the same structure as my_table without constraints and without data.

This was asked on Stack Overflow in How to drop all NOT NULL constraints from a PostgreSQL table in one go. It appears to give a good range of solutions.

The accepted answer by Denis de Bernardy is:

You can group them all in the same alter statement:

   alter table tbl alter col1 drop not null,
                   alter col2 drop not null,
                   …

You can also retrieve the list of relevant columns from the catalog, if you feel like writing a do block to generate the needed SQL. For instance, something like:

select a.attname
  from pg_catalog.pg_attribute a
 where attrelid = 'tbl'::regclass
   and a.attnum > 0
   and not a.attisdropped
   and a.attnotnull;

(Note that this will include the primary key-related fields too, so you'll want to filter those out.)

If you do this, don't forget to use quote_ident() in the event you ever need to deal with potentially weird characters in column names.